Well, if it happens after playing, then something you are doing while playing is the cause! As much as it may upset you to have it associated with your flute, it’s really a good thing, because you’ll be able to watch yourself while playing to see what’s causing it. Once you know what it is, you can avoid it.
If you’ve been playing Boehm flute for 25 years, something you are doing now, with the wooden flute, is different and that is likely to be the cause of your trouble. From your post, it looks like you already identified it.
As you know, the jaw opens and closes. We often think of this as occurring only vertically, but it also involves sideways motion. The lower jaw goes up and down, and to the left, and to the right. The muscles and ligaments which accomplish these actions can become strained and painful.
If you went out and ran too far, or climbed too many stairs, you’d expect soreness in your legs. In the same fashion, if you do too many repetitions of opening and closing, or lefting and righting, with your lower jaw, you’ll experience soreness. Think about it–if you chew gum too much, the muscles that open and close your jaw become sore. You’ll also get sore muscles if you keep them tense–think about the stiff neck and pain you can get from holding your head wrong for too long.
As has been suggested, a few days’ rest isn’t such a bad idea. You might also benefit from some ice to the area, perhaps alternated with a hot pack.
Relaxation, as Tal mentioned, is going to help. He’s also right about everything else he said.
Stretching will help, too. Muscles that get too tight hurt, and when they get too tight, they don’t relax, and that makes it easier to strain or injure them the next time, thus causing a vicious cycle. There are TMJ exercises and stretches on the net, but see if a plain old yawn helps.
Yawning is a great stretch. Even if you try to open your jaw as far as you can, a yawn usually does better. It’s hard to overstretch with a yawn, too.
A little massage will help, and I’ll tell you how to do that yourself. It’s really very easy, as you can get to the muscles involved all by yourself! This is an inside-outside affair, so you put one finger inside your mouth and one outside. That enables you to massage by working the muscle between your fingers.
If this is the left side, put your left hand up to your cheek. The index finger goes inside, between your back teeth and your cheek. The thumb is at the same place on the outside. Just pinch lightly. There is a strip of muscle running from about your cheekbone to your lower jaw. That’s the culprit.
You can feel it easily if you clench your jaw. You’ll feel it as it contracts and crushes your finger into your teeth. Once you’ve found it, you can massage it. Pinching it between your fingers, start as high up as you can reach and drag down as low as you can go. Move to a different spot and repeat. Keep doing that until you’ve done the whole muscle. Not too hard, either, so that you don’t cause pain just by squashing it.
This should help. It’s not likely to hurt. But, of course, here is the usual disclaimer to see a physician, etc., etc. If you are in the US, some massage therapists can help with this problem and others cannot, but if you can find one, it’s worth a visit. I don’t gather from your post that you’re that far gone, though.
